The present invention concerns a process for preparing DDTr-free 1,1-bis-(4-chlorophenyl)-2,2,2-trichloroethanol and formulations substantially free of the practically inactive isomer 1,1-(p-chlorophenyl)-(o-chlorophenyl)-2,2,2-trichloroethanol (o,p-dicofol).
The 1,1-bis-(halophenyl)2,2,2-trichloroethanols are miticidal agents, the preparation of which are described in U.S. Pat. Nos. 2,812,280 and 2,812,362. 1,1-bis-(chlorophenyl)-2,2,2-trichloroethanol (dicofol) is an effective acaricide and it and compositions containing dicofol are extensively used in agriculture and horticulture. The present commercial process for manufacturing 1,1-bis-(chlorophenyl)-2,2,2-trichloroethanol (dicofol) uses 1,1-bis-(chlorophenyl)-2,2,2-trichloroethane (DDT) as the starting material. DDT is dehydrohalogenated with alkali to afford 1,1-bis-(chlorophenyl)-dichloroethylene (DDE), which is chlorinated to afford 1,1-bis-(chlorophenyl)-1,2,2,2-tetrachloroethane (Cl-DDT). The 1,1-bis-(chlorophenyl)-1,2,2,2-tetrachloroethane is then converted via hydrolysis to the desired product, dicofol.
Technical dicofol made by this process contains from about 2% to about 10% (typically 7%) of DDT-related impurities (DDTr's).
The DDTr's which are encountered in the present commercial process to manufacture dicofol include: 1,1-bis-(4-chlorophenyl)-2,2,2-trichloroethane (p,p'-DDT); 1,-(4-chlorophenyl)-1-(2-chlorophenyl)-2,2,2-trichloroethane o,p-DDT); 1,1-bis-(4-chlorophenyl)-2,2-dichloroethylene (p,p'-DDE); 1-(4-chlorophenyl-1-(2-chlorophenyl)-2,2-dichloroethylene (o,p'-DDE); 1,1-bis-(4-chlorophenyl)-2,2-dichloro ethane (p,p'-DDD); 1-(4-chlorophenyl)-1-(2-chlorophenyl)-2,2-dichloroethane (o,p'-DDD); 1,1-bis (4-chlorophenyl)-1,2,2,2-tetrachloroethane (p,p'-Cl-DDT); 1-(4-chlorophenyl)-1-(2-chlorophenyl-1,2,2,2-tetrachloroethane (o,p'-Cl-DDT). Non-DDTr impurities which are encountered in the present commercial process used to manufacture dicofol include: 4,4'-dichlorobenzophenone (p,p'-DCBP); 2,4'-dichlorobenzophenone (o,p'-DCBP); 4,4'-dichlorobenzyl (p,p'-DCBZ); and 2,4'-dichlorobenzyl (o,p'-DCBZ). DDTr's are present along with the desired dicofol product due to the impurity of DDT used as a starting reactant and formation during the conversion of DDT to dicofol. As a group, DDTr's are suspected of posing an environmental risk.
Accordingly, it is desirable to find means to eliminate or reduce these DDTr impurities.
Recently, U.S. Pat. No. 4,705,902 described a process for preparing DDTr-free dicofol using selective solvent extraction. However, even the product of this extraction process is a mixture of isomers and still contains some 15% of the o,p'-dicofol. In addition, this product is a semi-liquid/waxy, odiferous, brown substance, which must be heated to a melt for dispensing and formulation and can only be shipped in drums, said drums then being a considerable environmental problem. The waxy state of the product also makes it very difficult to formulate as a flowable powder.